1. Field of the Invention
The present invention relates to an exhaust gas purification apparatus of an internal combustion engine.
2. Description of the Related Art
A selective catalytic reduction NOx catalyst (hereinafter, also referred to as an SCR catalyst) is known to be provided in an exhaust passage of an internal combustion engine. The SCR catalyst is a catalyst that selectively reduces NOx using a reducing agent. In addition, a technique is known in which a liquid injection valve that supplies a liquid reducing agent and a gas injection valve that supplies a gas reducing agent are respectively provided on an upstream side of an SCR catalyst and either the gas reducing agent or the liquid reducing agent is injected in accordance with an operating state of an internal combustion engine or the like (for example, refer to Patent Document 1).